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Simple, no-math transformer snubber using Quasimodo test-jig
Simple, no-math transformer snubber using Quasimodo test-jig
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Old 3rd November 2017, 12:52 PM   #1301
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
I haven't seen any measured data which suggests that mounting a transformer to a chassis, has any effect upon the damping factor zeta.

Since zeta depends upon Rdamping, Ltotal, and Ctotal {equation (A.10) in QM design note}, it seems reasonable to assume that if zeta changes, the reason might be that one or more of R, L, and C have changed. But first, study the measured data.
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Old 1st January 2018, 04:17 PM   #1302
rickmcinnis is offline rickmcinnis  United States
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Would it be just a matter of changing a capacitor to set QUASIMODO for 60 hz?

I know it is antithetical and beyond the pale but I have been working with half wave rectifiers on line amps and my phono amp and find there is something that is different in the background noise. Within brute force supplies (CLCLCLC) I have as much quiet as I did with all kinds of regulators including the JUNG DIDDEN reg but I was never sure if it was absolutely right since it seems to require a test bench to be sure it is operating correctly. and if I had one I would not know what to look for.

Just wanted to give a context. Inspired by the Marantz 7.

I would think snubbing a half wave would be just as important. Is this a simple mod to the QUASIMODO by any chance?
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Old 2nd January 2018, 02:16 PM   #1303
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Let's attempt to answer this question by studying the way an unmodified, "stock" Quasimodo works.

Please connect your Quasimodo to a transformer secondary, short all other windings, and remove the trimmer Rs from its socket. Thus Rs=Infinity and you ought to get a LOT of ringing. Adjust the vertical setting, trigger setting, etc., to get a nice tall legible display. Adjust the horizontal sweep rate so you can see the stimulus and the first few cycles of ringing. (I'm guessing this may take 1 usec/div to 10 usec/div). Take a scope photo / screen_capture of the scope face display and post it here, calling it Fast_Picture. Be sure to write down the horizontal sweep rate (or circle it in the scope picture if displayed).

Now change the horizontal sweep rate on your scope and make it slow enough that you can see two stimulus pulses on the scope face. This will probably require a setting in the neighborhood of 2 milliseconds/division or so. Take a scope photo / screen_capture of the scope face and post it here, calling it Slow_Picture. Be sure to write down the horizontal sweep rate (or circle it in the scope picture if displayed).

Once we have Fast_Picture and Slow_Picture, publicly posted here for all to see, we can analyze the situation.
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Old 3rd January 2018, 10:33 PM   #1304
rickmcinnis is offline rickmcinnis  United States
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As always, Mr. Johnson I know I am a child in comparison to your electronics abilities. I hope that doesn't sound curt because I mean it sincerely.

I am glad to do as you asked. I got an oscilloscope just be able to use QUASIMODO, the RIGOL that is inexpensive and many people say is good.

But being tentatively pokey using the thing I will wait until Saturday so I will have enough time to get it right.

You must understand being the eternal dilettante that I have to admit I am, my real understanding of electronics is very limited and I have done nothing more than what I needed at the moment to further it. Forgive me for hoping for a simple capacitor value substitution!

I know I need to get more comfortable with the 'scope so I will look forward to doing this and post the picture.
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Old 1st February 2018, 05:13 PM   #1305
jackinnj is offline jackinnj  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Mark -- did you ever consider building the "EMI Sniffer" -- starts on page 54 of Linear Tech ap note 70. http://cds.linear.com/docs/en/application-note/an70.pdf
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Old 1st February 2018, 05:32 PM   #1306
ArthurDK is offline ArthurDK
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Interesting subject - How to dampen rectifier noise, I suppose.

That must be the other part of building a noiseless PSU.


Br
Arthur.
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Old 1st February 2018, 05:42 PM   #1307
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
I bought one from Mr. Carsten himself! Dialled the phone number on the LT app note, he picked up, and we talked. I asked if he sold finished units and he said yes.

This was pre-Quasimodo, when I was searching for a way to measure rectifier-induced transformer ringing. Carsten's EMI sniffer turned out not to be what I wanted; it wouldn't give useful output when dialling the damping factor upwards towards zeta=1.0. And it required the transformer + rectifier + filter caps to be connected together & driving a heavy load. No problem for existing audio equipment, moderately painful for a brand new transformer straight out of the box.

A battery powered bellringer test jig + oscilloscope, gave me exactly what I wanted, and I found it to be very easy to use. So I retired the EMI sniffer probe.

(BTW I also bought some E-field and B-field probes from Vietnam after an enthusiastic review on EEVblog: (link to Youtube). Never did anything useful with them, however.)
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Old 1st February 2018, 08:23 PM   #1308
6L6 is online now 6L6  United States
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Simple, no-math transformer snubber using Quasimodo test-jig


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Old 1st February 2018, 08:25 PM   #1309
6L6 is online now 6L6  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
The Morgan Jones article can be found here -

Linear Audio | your tech audio resource
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Old 3rd February 2018, 02:28 PM   #1310
jackinnj is offline jackinnj  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Quote:
Originally Posted by Mark Johnson View Post

(BTW I also bought some E-field and B-field probes from Vietnam after an enthusiastic review on EEVblog: (link to Youtube). Never did anything useful with them, however.)
My world is now mostly below 10MHz.

I built a sniffer from a hard drive head and coil on a wooden dowel. Encased in a brass tube (Michael's Stores) which had two small slots.
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